Ultrasonic method

ABSTRACT

Ultrasonic apparatus for use in detecting an object having a transducer. The transducer has an array of at least one element coupled directly into air. The apparatus also includes a transmitter which may be multi-channel, a receiver which may be multi-channel, a transmit receive switch, and a computer for causing operation of said transmit receive switch to cause sequential supplying of pulses of energy from the transmitter to the element or elements of the transducer and for receiving energy received by the transducer. The element or elements of the transducer are provided with a roughened surface to produce high frequency ultrasonic energy.

This is a division of application Ser. No. 532,576 filed Sept. 15, 1983.

This invention relates to an ultrasonic apparatus, system and method andmore particularly to such an apparatus, system and method providing highrange resolution.

Heretofore ultrasonic apparatus and systems and methods have beenprovided. However, in general such apparatus, systems and methods havebeen characterized in that they utilized low frequencies and did notprovide a focused energy beam. It has been found that in many industrialprocesses there is a need for a ranging and noncontacting testingapparatus which utilizes a focused energy beam that can be utilized fordetecting the edges of objects and ascertaining the size and shapes ofobjects. A narrow energy beam is desired to accurately describe theprofile, topography, edge and other surface irregularities of an object.In order to obtain the great accuracy and detail of the target image itis desirable to have a beam of as small a diameter as possible.

In general, it is an object of the present invention to provide anultrasonic apparatus, system and method which has a high rangeresolution.

Another object of the invention is to provide an apparatus, system andmethod of the above character which utilizes focused energy beams inair.

Another object of the invention is to provide an apparatus, system andmethod of the above character using relatively high frequency soundbeams.

Another object of the invention is to provide an apparatus, system andmethod of the above character which is relatively inexpensive.

Another object of the invention is to provide an apparatus, system andmethod of the above character which is particularly applicable torobotics and industrial automation including handling of forestproducts.

Additional objects and features of the invention will appear from thefollowing description in which the preferred embodiments are set forthin detail in connection with the accompanying drawings.

FIG. 1 is a perspective view of an apparatus, system and methodincorporating the present invention and being utilized in a roboticapplication.

FIG. 2 is a schematic block diagram of a typical system incorporatingthe present invention.

FIG. 3 is a side elevational view of a transducer incorporating thepresent invention with certain portions being broken away.

FIG. 4 is a front elevational view of the transducer shown in FIG. 3looking along the line 4--4 of FIG. 3.

FIG. 5 is a cross-sectional view taken along the line 5--5 of FIG. 3.

FIG. 6 is a view looking along the line 6--6 of FIG. 5.

FIG. 7 is a rear elevational view of the transducer shown in FIG. 3.

FIG. 8 is an exploded view of the transducer shown in FIG. 3.

FIG. 9 is a graph showing the manner in which the diffraction of eachelement is directed towards the axis of the transducer.

FIG. 10 is a side elevational view of a mirror which can be utilized inconjunction with the transducer shown in FIG. 3.

FIG. 11 is a plan view of the mirror taken along line 11--11 of FIG. 10.

FIG. 12 is a graph showing the effects of the mirror of the type shownin FIGS. 10 and 11 being used in connection with a transducer of thetype shown in FIG. 3.

FIG. 13 is a plan view of another transducer incorporating the presentinvention.

FIG. 14 is a cross-sectional view taken along the line 14--14 of FIG.13.

FIG. 15 is still another embodiment of a transducer incorporating thepresent invention.

FIG. 16 is a block diagram of another system incorporating the presentinvention transmitting on multiple channels and receiving on a singlechannel.

FIG. 17 is a block diagram of another system incorporating the presentinvention transmitting and receiving on a single channel.

In FIG. 1 there is shown a robot 21 which is provided with an ultrasonicapparatus, system and method incorporating the present invention. Therobot 21 is controlled by a control system mounted in a console 22. Thecontrol console 22 contains electronics of the type hereinafterdescribed. Also included is a video monitor 23. The robot is providedwith a six axis (plus grasp) all electric overhead arm 24. An ultrasonictransducer 26 incorporating the present invention is carried by the armand is used for sensing information for operation of the arm.

In the application shown, the robot 21 is mounted along side a conveyor27 and has parts carried by as for example screws 28 and washers 29 atwhich are to be sensed by the transducer 26 in connection with theoperation of the robot 21. In a typical application, the robot has anecessity for locating and identifying the parts which are moving on theconveyor and thereafter picking up the parts and performing certainoperations with the parts.

Numerous methods can be used for identifying and locating objects inthree dimensions. The returned echos can be utilized for this purposesince the ultrasonic beam which is highly focused represents points inspace to provide imaging data for object recognition by a robot or otherautomatic device. This makes it easy for an end user to use a roboticvision system at a work place. This can be effected by taking anacoustic picture of an object with the scanning system mounted on aprecisely controlled robot. Sufficient views of the object can be takenwith the scanner to locate all unique features of the object. Thispattern is stored in a computer memory. The computer can be providedwith a graphics software capability which through the use of appropriatealgorithms can be used to provide a 90° translation of any view of afacet of the object or to revolve the object stored in the memory aboutany of its three axes and translate the shape, outline and objectposition by a single scan or scans of the complete object. Also it canbe used to store in the memory the precise coordinate location of therobot stored. All of this can be accomplished without the need forsophisticated software or applied mathematics on the part of the user.

In FIG. 2 there is shown a system in block form showing the componentsnecessary to provide a computer with ranging information for operationof the robot. As hereinafter explained, the transducer 26 includes oneor more elements or rings which are simulated at 31 and which areconnected by conductors 32 to a transmit-receive switch 33. The transmitand receive switch 33 is provided to permit the receivers andtransmitters of the system to communicate with the transducer 26 atappropriate intervals of time. The transmit receive switch 33 is of aconventional construction and is connected to a four-channel transmitter34 and a four-channel receiver 36. The transmit receive switch 33establishes the timing for sequential communication with the transducerby the transmitters and receivers 34 and 36. The transmitters 34 andreceivers 36 are provided with a suitable D.C. power supply 37 with avoltage ranging from 100 to 550 volts but preferably approximately 450volts. A bidirectional address/data bus 38 establishes communicationbetween a single board computer 39 and interface block 41 which is incommunication with a host computer 42 through a bus 43. Thebidirectional address data bus also establishes communication betweenthe single board computer 39 and the four-channel transmitter 34 and thefour-channel receiver 36 as well as a receiving beam former 44 withdetector. A local one-way bus 46 is provided for establishingcommunication between the four-channel receiver 36 and the receivingbeam former 44.

The four-channel transmitter is provided with delay generators andaccepts data bus commands for delay times on each transmit ring andaccepts firing commands from the same bus. Transmission is delayed on atleast three of the four channels to create a focused effect by the useof the delay generators. The transmitter 34 is capable of running in afree running mode. When this is the case, it will transmit on all fourelements or rings using standard delay times so as to weakly focus theenergy beam to provide a large depth field. When it is desired to lookat an object more closely, the depth of field can be decreased under thecontrol of the single board computer 39 to specifically focus theultrasonic energy into a particular region. Alternatively, a singlesearch pulse can be sent out to determine the target range. Using thisrange data transmitter delay times can be set in order to focus allenergy at a point in space in transmission. Three modes of operation arepossible: (1) weakly focused transmit, hard focused recive, (2) sharplyfocused transmit, weakly focused receive and (3) sharply focusedtransmit, sharply focused receive. Modes (1) and (2) produce equallateral resolution and (3) produces greater accuracy. Modes (1) and (2)are less expensive and easier to implement whereas mode (3) is morecostly.

The four-channel receiver 36 is comprised of four substantiallyidentical amplifiers having a band width of 50 percent with a centerfrequency on the order of 250 kilohertz. The band width provided makesit possible to receive echos which are amplified and then sent to thereceiving beam former 44. The four-channel receiver is provided with aboard multiplex bus. The beam former 44 introduces electronic delays ina manner well known to those skilled in the art to compensate for thedifferent path lengths of the received echos which in effect iselectronically changing the focal length of the acoustical detector. Thereceiving beam former 44 with detector will provide an output on thebidirectional address/data bus to the effect that an echo has beenreceived at a particular point in time which will be recognized by thesingle board computer 39 as a returned echo. As explained earlier, thesingle board computer directed the transmitter to supply a pulse at timezero and then begin counting on its internal clock until an echo isreceived. It then converts that time into a path length which issupplied through the interface 41 to the host computer 42. Thus it canbe seen that the single board computer causes firing of the transmitterand after receiving information from the receiver 36 through thereceiving beam former 44 with detector calculates the range of theobject being viewed.

The interface block 41 makes it possible to automatically output rangedata from over two inches to 12 inches in range. The interface block 41can be utilized to focus the transmitter at a predetermined range. Theinterface block 41 upon request will pass data from each channelseparately. The single board computer 39 can be utilized to performdiagnostics to transfer data, store look up tables and calculate delays.

The four-channel receiver 36 receives information from each ring orchannel. It amplifies and filters each channel to give a signal at a 12inch range with a flat target with low noise. The four-channel receiverwill accept multiplex control from the beam former 44. It also suppliesan output to the beam former through the local one-way bus 46. Thereceiving beam former 44 listens to the four-channel receiver 36 throughthe local one-way bus. It sums the information in each channel to give aformed output. The beam former can also accept data bus commands and topass only one channel if desired (for diagnostics). It has a digitalthreshhold detector and places a pulse on the bidirectional address/databus 38 whenever an echo comes in. Typically it is provided with threememories which can be utilized for storing the amplitudes of each of upto three echos. It dumps the amplitudes of each of the three echos o tothe bidirectional address/data bus 38 at the request of the single boardcomputer 33.

The acoustical transducer 26 used in the present invention is shown indetail in FIGS. 3 through 8. As shown therein, the transducer 26consists of a cylindrical annulus or body 51 which is provided with acylindrical central opening 52. A flexible sheet or foil 53 is stretchedover the opening 52 and is clamped in place by a clamping ring 54 whichis secured to the body 51 by a suitable means such as screws 55 threadedinto bores 56. The sheet or foil 53 is comprised of a suitable flexiblefilm of insulating material such as polypropylene having a thicknessranging from 6 to 10 microns upon which there is evaporated a thin layerof a suitable conducting material such as aluminum or gold to provide aresistivity of 2-4 ohms per square. The aluminum layer can have athickness ranging from 50 to 300 Angstroms and typically has a thicknessof approximately 200 Angstroms. Resistivity up to approximately 200 ohmsper square can be tolerated with the lower limit being zero. The foil orfilm 53 must be sufficiently thin to act as a sensitive receiver andalso have a high dielectric constant so it has the capability ofwithstanding the high bias voltage. Typically the films can be ofplastic as, for example, Kapton having a thickness of 0.0003 inches, apolypropylene having a thickness of 0.0004 inches and Teflon having athickness of 0.00025 inches. Each of those were found to operatesatisfactorily to produce ultrasonic frequencies up to 500 kilohertz.

A circular relatively rigid backing plate 57 is provided which is formedof a suitable non-conductive material as, for example, a plastic havinga suitable thickness as, for example, one-quarter of an inch. Aplurality of elements having conducting surfaces are mounted upon thisbacking plate 57. As shown on the drawings, the elements consist of acenter element in the form of a cylinder 58 and three additionalelements in the form of concentric rings 59, 61 and 62 to provide for atotal of four elements, all of which are secured to the backing plate 57by suitable means such as screws 63. In the arrangement shown, threescrews 63 spaced 120° apart are provided for securing each of the rings59, 61 and 62 to the backing plate 57. As can be seen, the elements 58,59, 61 and 62 have conducting surfaces which lie in a plane parallel tothe top surface 65 of the body 51 and also parallel to the planarsurface 66 formed on the backing plate 57. The elements or rings 59, 61and 62 are provided with inwardly extending annular lips 59a, 61a and62a which are secured to the backing plate 57 by screws 63 which arecountersunk in holes 67 provided in the backing plate 57 and arethreaded into threaded holes 69 in the lips 59c, 61a and 62a and in theelement 58. The backing plate 57 with its elements 58, 59, 61 and 62carried thereby is secured to the body 51 in a suitable manner. Forexample, as shown, a rear shroud 69 in the form of a circular plateformed of a suitable material such as metal is secured to the body 52 byscrews 71 extending through mounting holes 72 and threaded into threadedbores 73 in the backing plate 57 as well as into threaded bores 56 inthe body 51. An electrical connector 74 is mounted in the rear of theshroud 68 in a hole 75 and is connected by suitable coaxial wires (notshown) to the screws 63 to form electrical connections to the elements58, 59, 61 and 62. As hereinbefore explained the polypropylene foil 53is mounted in such a manner that the non-coated or insulating side facesthe elements 58, 59, 61 and 62 and the coated side faces away from theelements.

A screen 76 formed of a suitable material such as steel wire mesh as,for example, 1/8th or 1/4 inch mesh overlies the plated side of thepolypropylene foil 53 and serves to protect the foil 53. A rubberannular gasket 77 overlies the clamping ring 54 and the screws 56. Acircular front shroud 78 is provided which is L-shaped in cross sectionhas an annular lip 79 overlying the outer margin of the screen 76. Thefront shroud extends over the body 51 and is secured thereto by screws81 extending into threaded bores 82 provided in the body 51.

The surfaces 64 of the elements 58, 59, 61 and 62 are treated in aparticular manner to achieve the particularly desirable results of thepresent invention. The elements 58, 59, 61 and 62 are formed of asuitable conductive material and preferably are formed of an aluminumalloy. One aluminum alloy found to be particularly satisfactory isidentified as alloy 5086-T-116. This is a corrosion resistantmarine-type alloy. The elements 58, 59, 60, 61 and 62 were all machinedfrom a sheet of aluminum alloy having a thickness of one-half inch orgreater. As can be seen, the element 58 is formed as a cylindricalpiston whereas the elements 59, 61 and 62 ar formed in the manner shownwhich is substantially L-shaped in cross section. The surfaces 64 of theelements were polished to an optical shiny finish. This is accomplishedby utilizing sandpaper and a polishing cloth in a lathe.

After this optically shiny finish had been achieved, the elements 58,59, 61 and 62 were treated with a ferric chloride solution. This wasaccomplished by purchasing a commercial ferric chloride and diluting thesame with water. The ferric chloride (Fe₂ Cl₃) was diluted withone-third water to provide a solution of 66 2/3% ferric chloride and 331/3% water. The dilute ferric chloride was placed in a container at roomtemperature and pressure. The surfaces 64 were etched in this solutionby repeatedly dipping the elements into the solution for a period oftime ranging from 2 to 3 minutes. Preferably this accomplished byintroducing the elements into the solution for periods of one minuteeach, removing the same and drying them to examine the etching on thesurfaces 64. Typically to obtain the desired frequency of operation forthe transducer 26, it has been found that the dipping should occur twoto three times at one minute each to achieve the desired roughness ofthe surfaces 64. It has been found by way of example that just a oneminute etch will give a frequency of 300 to 400 kilohertz (300-400 khz).Further etching provides a further roughness and will give a resonantfrequency of approximately 250 kilohertz. In performing this dippingoperation it has been found that it is desirable to mount the elements58, 59, 61 and 62 on the backing plate 57 and to dip the entire assemblyinto the etching solution. It is believed that this etching providesroughened surfaces 64 which underlie the unplated side of the foil 53.Alternatively, the roughened surface can be obtained, although not aseffectively, by sandblasting, machining or scrubbing. The roughenedsurface formed by etching is provided by an aluminum oxide layer of athickness determined by the etching time. Since this aluminum oxidelayer has insulating properties it serves as an additional dielectriclayer.

The upper frequency limit is determined by (a) the thickness of the film(film thickness is inversely proportional to frequency) and (b) thesurface finish of the solid metal plate of the capacitor (the smootherthe surface finish the higher the frequency). Higher frequencies aredesirable in order to achieve improved lateral and ranging resolutioncapabilities. However, it should be appreciated that the attenuation ofsuch higher frequencies increases greatly as the frequency increases.

After the etching operation has been completed, the foil 53 is stretchedover the annular body 51 and clamped in place by use of the clampingring 54. Thereafter, the backing plate 57 with the elements securedthereto is inserted so that the surfaces come into engagement with thefoil.

With the electrical connections hereinbefore described, the frontsurface or plated side of the foil 53 is at ground potential whereas theelements 58, 59, 60 and 61 which are connected by the coaxial cables(not shown) to the transmit receive switch 33 are above ground so thereis in effect provided a capacitor in which the metal coating on one sideof the foil 53 serves as one metal plate, the polypropylene of the foilserves as an insulator and the surfaces 64 serve as the metal plate onthe other side of the insulator to provide what can be considered aSell-type transducer.

The transducer 26 after it has been assembled in the manner hereinbeforedescribed and is connected to a system of the type described in FIG. 2is pulsed with a high voltage typically in the vicinity of 100-500 voltsthat is applied between the grounded front surface of the foil 53 and anelement of the elements 58, 59, 61 and 62.

In an operation, the application of high voltage between a ring orelement and the front surface of the foil creates an attraction betweenthe ring and the foil. This movement of the foil at high frequenciescreates the ultrasonic energy utilized in the present invention. It hasbeen found that as the voltage is increased, the signal to noise ratiois enhanced with respect to the returned echos. The change in voltagehowever has no appreciable effect on the frequency. It is, however,generally desirable to utilize as high a voltage as possible.

In the present invention the frequency of operation is controlled by (1)etching on the capacitor plate, and (2) external series inductance and,(3) film thickness. The beam former as used in the present inventionshapes the sound beam and dynamically focuses the sound beam in transmitand receive at any point on the axis of the array to achieve highlateral resolution. In the beam former the signals from the arrayelements are delayed to produce a soft transmit focus over a large depthof field. Because of these delays, signals from each element will arriveat a target on the axis of the array roughly in phase, i.e., focused.Alternately, signals can be delayed in transmit to arrive at a point onthe axis of the array at the same time to achieve focusing. If theobject distance is known, a very precise focus can be achieved byappropriate delays. Alternatively, if object distance is unknown, a softfocus of a large depth of field can be used or a single search pulse canbe transmitted to determine range.

The receiving beam former with detector 44 listens to the incomingsignals through the local one-way bus 46 It sums the signals on eachchannel to give a formed output. It also can receive address/data buscommands that pass only one channel if desired as, for example, fordiagnostic purposes. It has a digital threshold detector and dumps pulseinformation on the address/data bus whenever an echo is received. It isprovided with three memories to store the amplitude of each of the echosup to 3 echos. It dumps the amplitudes of the echos onto theaddress/data bus at the request of the signal board computer 39.

The transmission pattern generated by the phased array transducer 26 isshown in FIG. 9. As hereinbefore explained, the phased array is asubstantially conventional Sell-type transducer of annular design. It isprovided with a central element 58 which is disc-like in conformationrather than being in the form of an annulus whereas the elements 59, 61and 62 are in the form of annuli with the annuli decreasing in radialthickness the nearer they are to the cuter extremity of the annulararray. Thus the outermost ring or annulus has the thinnest radialmeasurement.

The transmission pattern of ultrasonic energy from each of theseelements is indicated by the lobes 101, 102, 103 and 104 with lobe 101being associated with the central element 58 and the side lobs 102, 103,and 104 being associated with the elements 59, 61 and 62 respectively.The size of the central element or disc 58 is chosen to provide a mainlobe 101 which generally corresponds t the desired field of view for thetransducer 26 and provides the minimum usable range. The elements 59, 61and 62 provide ultrasonic energy transmission in the form of main lobes102, 103 and 104 in which the main lobe 102 has the smallestdiffraction, main lobe 103 has medium diffraction and the main lobe 104has large diffraction. As is appreciated by those skilled in the art,the farther the element is from the center of the array, the greater thediffraction required in order to have the energy be diffracted towardsthe axis of symmetry of the array. In other words, all the elements ofthe array must be able to diffract energy towards the axis of the array.The central element 58 generally has a diameter which is approximately20% of the array diameter in order to provide the narrow beam or mainlobe 101. The transducer can be of any suitable size as, for example, acylinder having a diameter of approximately four inches and an actualthickness of approximately three quarters of an inch.

In operation of the transducer 26 in a robotics application as shown inFIG. 1, the transducer 26 is mounted in the scan head carried by the endof the robot arm 24 to give the scan head a field of view whichcorresponds to the work area of the robot arm 24 of the robot 21. Thescan head 26 can be moved by the arm 24 across the object which in thiscase may be a bolt 28 or a washer 29 to determine as many points orspots on the object being scanned as are required to establish the trueshape of the object. The position of the scan head 26 is known since theposition of the robot 21 is known.

The system which is shown in FIG. 2 sends out pulses of high frequencysound from the transducer or scan head 26 and receives high frequencysound reflected by the object being scanned. The system shown in FIG. 2also measures the time of flight to and from the object being scannedand converts this into range data since the speed of sound in the air isknown. Only a very small portion of the object being scanned can bescanned at any one time to ensure that specific features of the objectcan be seen. The narrow shape of the sound beam is achievedelectronically through the use of the beam former 44. The beam former 44utilizes time delays on both transmit and receive to constructivelyphase transmit and receive signals from individual array elements sothat a dynamically focused energy beam is obtained. Each of the arrayelements in the transducer 26 has a known position in the array. Bytiming the transmission of the signal from each of the array elements,all signals can be made to arrive at a point in space, on axis, at thesame time. Conversely each element of the array can receive a signal atthe same time if a delay, based on this position, is imposed on eachelement. Because of the array geometry and the timing delays used,signals can only be constructively added at a known position in space toachieve the desired information.

As hereinbefore explained, the scan head transducer 26 serves as anelectrostatic transducer which is used to both transmit and receiveaccoustic signals. It is comprised of metalized foil 53 which is engagedby radial surfaces of concentric array elements 58, 59, 61 and 62. Oneside of the foil 53 serves as one plate of a capacitor with the filmitself being the dielectric of the capacitor and with the metallicsurfaces 64 of the array elements being the opposite plate of thecapicator. The active area of the array is the surface area 64 incontact with the film or foil 53.

The physical aspects of the array are determined by the overall lateralresolution desired, physical size limitations of the aperture, operatingfrequency and how close into the center of the array the target orobject must be seen. Some of these factors are not mutually exclusive.For an array to have a large aperture, the outer ring must have adiffraction pattern such that its half beam width which will illuminatea target at the closest desired point to the array. For a four inchaperture and a specification to see a target at two inch actual distancefrom the array, the element width must be roughly 0.024 inches. Thisvery narrow element width results in a lack of receiver sensitivitybecause very little signal can be received. To overcome this limitation,the element width has been increased sufficiently, so that it will be agood receiver.

With a system and apparatus and method of the above character it hasbeen possible to provide vision quality accoustic imaging on a real timebasis which is particularly useful for robotic applications. Each of theelements of the phased array serves as a separate electrostatictransducer which when all four lobes are combined produce a highlydirectional ultrasonic beam.

As hereinbefore explained, it may be desirable to make the outer annularelement of an annular array thicker or having greater radial dimensionin order to make it possible to use more power in the transmitter andalso to provide additional receiving area and thereby improve the signalto noise ratio and as a consequence improve the range resolution.However, as soon as a thicker outer ring is utilized, the thicker thering the less it will diffract its energy into the desired locationalong the center axis of the array until a substantial distance from thearray which would make it very difficult for the transducer to image anobject which was very close in. Because of the attenuation in the air,it also would be difficult to receive echos from the object located at aremote distance. With apparatus of this type, it has been found that itis possible to readily image objects of various sizes. For example, ithas been found that a wire 0.007 inch in diameter which is locatedapproximately one foot in front of the transducer can be readily imaged,utilizing a broad band pulse having a center frequency of approximately250 kilohertz and a 50% band width.

Another embodiment of the invention is shown in FIGS. 10 and 11 in whicha transducer 26 has a mirror 111 mounted thereon. The mirror 111 can beformed of a cylindrical body 112 of a suitable material such asaluminum. A recess 113 extends through the central portion of the body112 and is in the form of a truncated cone which extends through theupper and lower surfaces 114 and 116 of the body 112. The surfaceforming the recess 113 is relatively highly polished and is providedwith a suitable angle so as to act as a mirror for reflecting ultrasonicenergy from the surface 64 of an outer annular element 62a. The mirror111 can be secured to the transducer 26 in a suitable manner such as bythe use of L-shaped brackets 117 secured to the body 112 by suitablemeans such as welding and secured to the transducer 26 by suitable meanssuch as screws 118. The use of the mirror 112 makes it possible to bendthe beam pattern from the annular element towards the axis of the phasedarray and therefore makes it possible to use an element having a greaterthickness in a radial direction for the reasons hereinbefore pointedout.

Although in FIGS. 10 and 11 only a single mirror 111 has been utilizedfor the outer annular element 62, it should be appreciated that mirrorscan be also utilized for the other annular elements in the array. Thusas shown in FIG. 12, additional mirrors 121 and 122 can be provided forthe annular elements 61 and 59. This makes it possible to make theelement 61 with a greater thickness. Also the element 59 can be made ofa somewhat greater thickness. As indicated by the rays shown in FIG. 12,the mirrors serve to bend at least certain of the ultrasonic raysemerging from the elements in a direction so that they are focused alongthe axis of the annular array. The nearest usable range for the annulartransducer is the one where the energy from each element can be focusedinto the axis of symmetry for the array. The mirrors permit the use oflarger than standard elements and therefore permit the use of greaterpower. They also make possible an improved signal to noise ratio forreception thereby improving the range, resolution and accuracy of thephased array.

In FIGS. 13 and 14, there is shown a mirror structure 126 which isparticularly applicable when a multiplicity of mirrors are used inconjunction with a phased array. Thus as shown in FIGS. 13 and 14 thereis provided a body 112 which is provided with the mirror surface formingthe recess 113. A support structure 127 is mounted within the recess 113and is provided with three legs 128 which are joined at the center andwhich are mounted in the body 112. The mirrors 121 and 122 shown in FIG.12 can be mounted upon this structure 127 in a suitable manner such asby having the legs 128 extend through openings provided in the mirrors121 and 122 which as shown are mounted so that they are disposed atpredetermined angles so as to provide the appropriate reflection for thebeams from the associated elements of the array. As with the surface113, the surfaces provided by the mirrors 121 and 122 are geometricallyrepresented by truncated portions of a cone. The surfaces 113 providedby the body 112 and the surfaces provided on the mirrors 121 and 122need not necessarily be provided by metallic surfaces. It is, however,necessary that these surfaces not absorb sound but they reflect sound.Thus in addition to being made out of metal, they also can be made outof plastic and even paper if it has a relatively hard surface which willnot absorb sound.

Another embodiment of the invention is shown in FIG. 15 in which atransducer 131 is shown. The transducer is of a type hereinbeforedescribed but is provided with only three elements rather than the fourelements of the previous embodiment. Thus it consists of a centralelement 132 which can be in the form of a cylinder, an intermediateannular element 133 and an outer element 134. The elements 133 and 134can have a radial thickness greater than the normally calculated radialthickness for such an array so as to make possible greater transmittingand receiving capabilities as hereinbefore described. In order to makethis possible, an accoustic horn structure 136 is provided. This hornstructure is provided with accoustic passages 137 and 138 which areassociated with the elements 134 and 133 respectively. Each of theaccoustic passages includes an inner horn-like passage 141, which islarge enough to encompass the radial dimension of the annular element134 and narrows down to an accoustic wave guide 142 which opens into anouter horn-like passage 143. Thus it can be seen that there is provided,in effect, a double horn-like configuration which serves as a soundbender to bend the sound waves so that they are directed onto the axisof the array within a relatively short distance from the array. As canbe seen from the arrows in FIG. 15, the double horn structure serves totake the ultrasonic energy from the annular elements 134 and to narrowthem down into an acoustic wave guide and thereafter expand the same ina different direction so that they are focused onto the axis of theannular array of the transducer 131. From the front side it can be seenthat the acoustic horn structure 136 will have concentric openings orslots through which the sound will pass. The acoustic horn structure canbe formed out of any suitable material which does not absorb sound as,for example, metal or plastic.

Although the present invention has been described primarily inconnection with robotic applications, it should be appreciated that theapparatus, system and method of the present invention can also beutilized in other fields as, for example, the medical field. The horn,lens or mirror structure will provide significantly better imagingquality, particularly on the outer rings of a medical annular phasedarray where these outer rings tend to be thinner than the inner rings.The robotic applications hereinbefore described have been applicationsin which imaging is through air. In the medical field the imaging isvery often through liquids such as water or other body liquids. The useof mirrors and horn structures hereinbefore described in medicalapplications makes it possible to provide apparatus in which moretransmitting power could be applied and more sensitivity could beobtained with respect to sound energy that is received to therebyprovide a sharper image from a deeper field. Alternatively, lenses canbe used in such applications.

Another system incorporating the present invention is shown in FIG. 16and consists of four elements 31 of a transducer of the typehereinbefore described which are connected to a transmit receive switch33. The transmit receive switch 33 is connected to a single channelreceiver/detector 151 which is connected to a single element 31 as, forexample, the central element. The output of the receiver 151 isconnected to a block 152 which includes an input-output (I/O) computerinterface, a timer and transmit delay tables. The block 152 is connectedto the computer bus output of a conventional type computer such as onehereinbefore described. The block 152 is also connected to a pluralityof delay generators 153 operating as beam formers. The delay generators153 are connected to a multi-channel transmitter 154 which is connectedthrough the transmit receive switch 33 to the multiple elements 31. Thusit can be seen that there has been provided a system which utilizesdynamic (variable) transmit focusing for focusing ultrasonic energyemanating from the transducer formed by the elements 31. By providingsuch dynamic focusing, it is possible to first weakly focus over arelatively broad area and then after the first echo is received,determine the range of the object. Thereafter the focus is sharpened sothat the ultrasonic energy is focused onto a small area which is in theimmediate area of the object being sensed. In this way, it is possibleto obtain high resolution of the object. The use of a single channelreceiver in this system greatly simplifies and reduces the cost of thesystem.

Still another embodiment of a system incorporating the present inventionis shown in FIG. 17 in which a single transducer element 31 is usedwhich is connected to a transmit receive switch 156. The transmitreceive switch 156 is connected to a single channel receiver/detector157. The receiver/detector 157 is connected to a timer board 158 whichincludes time of flight or target range capabilities. This board 158 isconnected to a digital range display 159 of a conventional type. Thetransmit receive switch 156 is also connected to a transmitter 151 whichcan be free running or pulsed. It is connected to the timer board 158and supplies timer synchronizing pulses to the timer board 158.

As can be seen the system shown in FIG. 17 is simplified over that shownin earlier embodiments of the invention. It has only one channel forboth transmit and receive. A single piston transducer as, for example,one of one inch in diameter can be utilized for the element 31. Thelateral resolution provided by a system such as that shown in FIG. 17 isinferior to that which is provided with the systems hereinbeforedescribed. However, the system shown in FIG. 17 is advantageous incertain applications where it is desired to provide a low cost simplesystem where only range to target information is desired. For example,the edge detection of boards in a lumber mill is an application for sucha system.

What is claimed is:
 1. In a method for treating a metallic element foruse in a capacitive-type transducer having first and second plates inultrasonic apparatus for generating ultrasonic energy, providing theelement with an optically shiny surface and chemically etching thesurface so as to roughen the surface whereby that surface can beutilized for generating ultrasonic energy when said metallic element isused as one of the first and second plates of the capacitive-typetransducer.
 2. A method as in claim 1 wherein the element is formed ofan aluminum alloy and wherein the etching is carried out by use of anetch of ferric chloride.
 3. A method as in claim 2 wherein said aluminumalloy is 5086-T-116 and wherein said ferric chloride etch is formed ofapproximately two-thirds ferric chloride and approximately one-thirdwater.
 4. A method as in claim 3 wherein said elements are treated withsaid ferric chloride solution for periods ranging from 30 seconds toapproximately three minutes.
 5. A method as in claim 4 wherein saidetching step is carried out at room temperature and at atmosphericpressure.
 6. A method for treating a metallic element for use in acapacitive-type transducer having first and second plates in ultrasonicapparatus for generating ultrasonic energy comprising the steps ofproviding a planar surface on the element, and forming sandpaper-likegrooves in said planar surface for producing ultrasonic energy when saidelement is used as one of the first and second plates of thecapacitive-type transducer.
 7. A method as in claim 6 wherein saidelement is formed of an aluminum alloy.